The present invention relates to systems and methods for treating process material and, more particularly, to systems and methods for treating municipal solid waste material, medical waste material, reclaimed paper and the like.
This process typically involves sterilizing high density materials such as glass, plastics, metals and recovering others from municipal solid waste (MSW) and converting paper, cardboard, food waste, etc. to a usable fiber and separating it from other recyclable materials.
As a result of increasing scarcity of landfills and more stringent environmental regulations, efforts have been made to reduce the volume of process material, such as municipal solid waste (MSW) and paper material, such as newsprint and other reclaimed and recycled paper products as a step in the process of disposing of the material, either by depositing it in landfills, incinerating it or recycling it.
Systems and methods have been developed to break down such material for disposal, or in the case of paper products, use as insulation, or for further processing to produce a combustible product.
A waste autoclave is a form of solid waste treatment that utilizes heat, steam and pressure of an industrial autoclave in the processing of waste. Saturated steam is pumped into the autoclave at elevated temperatures. The pressure in the vessel is maintained at for a temperature-dependant period to allow the process to fully ‘cook’ the waste. The autoclave process gives a very high pathogen and virus kill.
The ‘cooking’ process causes plastics to soften and flatten, paper and other fibrous material to disintegrate into a fibrous mass, bottles and metal objects to be cleaned, and labels etc. to be removed.
Rotating waste autoclaves provide mechanical forces to further process the waste. With rotation, the cellulose fibers (in paper, cardboard, and yard wastes) are mechanically and thermally pulped, analogous to the process known as thermo-mechanical pulping in the pulp and paper industry.
After ‘cooking’, the steam flow is stopped and the pressure vented. When depressurized, the autoclave door is opened, and by rotating the drum the ‘cooked’ material can be discharged and safely and easily separated by a subsequent series of screens and recovery systems. Consequently, a waste autoclave system can serve as a functional alternative to landfills, providing benefits of recycling of clean and sterile materials recovered from municipal wastes.
A basic invention for municipal waste autoclaves is found in U.S. Pat. No. 4,540,495 (Holloway, 1985) and is now in the public domain. This application describes inventions that improve the functionality of waste autoclave systems.
The present invention accordingly represents an improvement over prior art apparatus and methods, such as those described in U.S. Pat. Nos. 5,540,391; 5,126,363; 5,253,764; 5,190,226; 5,361,994; 5,427,650; 5,407,809; 5,636,449; 5,655,718; 6,397,492, and 7,347,391, all of which are incorporated herein by reference. PCT application PCT/US06/16773 and co-pending patent application Ser. No. 11/716,101 are also hereby incorporated herein by reference. Autoclaves generally require substantial “overcooking” to assure that the heterogenous materials in the autoclaves are properly treated. Hospital autoclaves, for example, typically use either a vacuum to remove air, or cautiously use density gradients to allow the removal of cool air as hot steam is introduced . . . both methods to provide some assurance that the contents are all exposed to steam. Further, test strips are also used to confirm that the (preset) cooking cycle achieves the desired organism kill.
Rotating waste autoclaves eliminate some of difficulties of heterogeneous materials by tumbling and comminution of the waste components. However, municipal waste is highly heterogeneous in nature. Single vessel components, for example, might include a large box of frozen food that has been insulated by paper, and/or a mass of putrescible waste rolled up in a carpet.
While the mechanical processes of a waste vessel help in assuring that the waste components each receive proper treatment, to date vessel systems have specified a long-duration fixed-duration cooking cycle in order to provide such assurances. Fixed-time cooking cycles will either under-treat or over-treat wastes, and neither outcome is desirable.
In a co-pending patent application Ser. No. 11/981,144 (and hereby incorporated herein by reference), there is disclosed a method for time-tracking of temperature contents in order to allow the treatment system to achieve an overall goal of a desired kill fraction. The system of the present invention as described herein provides a systematic process to assure that the various components of the vessel load each achieve a desired treatment level.
In essence, the vessel of the present invention may include the provision of a multiplicity of content temperature monitoring sites, such as thermocouple wells. The term thermocouple well is used henceforth, but it conceptually includes all temperature monitoring equipment.
The multiplicity of sites allows the temperature to be determined at a number of points, both circumferentially and longitudinally. A control system is provided to track the temperature (and the rate of change of temperature) at each of these thermocouple wells.
Variations between wells are signals that the waste treatment provided is not yet uniformly received by the non-homogenous wastes. The decision point to terminate the process is developed when the signals from the array of thermocouple wells are in agreement. The control system is provided with adaptive programming so that equipment biases between the various thermocouple wells, and or individual thermocouple failures, can be factored out of the decision process.